Bright annealing of metals



July 21, 1931. R. c`.. GUTHR'IE ET AL 1,815,505

BRIGHT ANNEALING OFMETALS u Filed Nov. 15. 1929 Patented July 21, 1931 lUNITED STATES ROBERT G. GUTHRIE AND OSCAR. J'. WOZASEK, OF CHICAGO,ILLINOIS, ASSIGNORS TO PEOPLES GAS BY-PRODUCTS CORPORATION, OF CHICAGO,ILLINOIS, A CORPORATION OF ILLINOIS; SAID WOZASEK NOW BY CHANGE' OF NAMEOSCAR J'..WILBOR PATENTl orf-'ica .BRIGHT ANNEALING OF METALSApplication led November 15, 1929. Serial No. 407,438.

This invention relates to improvements in the art of the brightannealing of metals simultaneously with a cleaning of the surface of themetal.

It has heretofore been proposed to anneal metals in the presence ofinert or nonoxidizing gases, whereby the metal is prevented fromtarnishing or oxidization on its surface. It has also been proposed tofollow the definite annealing operation b a scouring or pickling torestore the brig t surface to the metal.

In distinction from such processes, the present invention is competentof operation with a metal which may have either oxide or carbonaceoustarnish or discoloration on its surface, so that the metal is definitelyrestored, under practically all conditions, to a bright clear surfaceduring the time of annealin By annealing hereinafter will be understooda heating operation to which a metal is subjected, usually to soften itafter a cold working such as rolling, forging, etc.

It will be understood that a bar of metal upon passing through a rollingmill in which it has been reduced in cross section, becomes very hard,so that a further reduction by rolling would result in breaking orcracking of it, unless an annealing operation be interposed.Furthermore, the usual exposure of the hot bar, previous to cooling tothe atmosphere, results in a superficial oxidation at some parts, whileother parts are coated with a film of oil or carbonaceous matter fromthe rolls.

In order to remove these discolorations and superficial films, it isproposed according to the present method to successively subject themetal to an oxidation treatment and then to 'a reduction treatmentduring the course of the annealing.

The oxidation is accomplished by heating the metal to an annealingtemperature such as 1300" F., and causing it to come into contact withan oxygen-bearing gas such as carbon dioxide, air, oxygen, steam, fluegas or the like. This oxidizing gas then operates superficially upon themetal to burn ofl' any oil or other carbonaceous matter which may `lessstabley illuminants have been removed by some suitable method. Byremoving these less stable materials the deposit of carbon upon'themetal is hindered and prevented, so that by a careful regulation and.observation of the gases in the reducing phase, whereby the freedomfrom soot is attained, it is possible to produce a reduction of thesuperficial film of oxide, resulting in a bright clean surface for themetal.

rI his pre-treatment of the reducing gas to be employed, whereby theless stable so-called illuminants are removed, may be accomplished inseveral ways. It will be understood that the less stable hydrocarbons,of the unsaturated series, are what give the particular gas its directilluminating quality since these hydrocarbons crack or split duringcombustion and yield ofi1 particles of carbon and molecules of moresaturated hydrocarbons: the particles of carbon become incandescent andcause they yellow flame produced in the burning of standard city gas,for example, throughan ordinary jet. This same cracking occurs at theheat of annealing when such unstable hydrocarbons are present, andresults in a deposit of the carbon as soot u on the surface of themetal. It is there ore necessary to remove these hydrocarbons beforebringing the gas into contact withv the hot metal.

The gas may be passed through paraffin or similar oils for dissolving orabsorbing the unsaturates from the gas: or the as may be vpassed overheated charcoal or co e.' lVith either of these operations, it is foundthat practically no carbon deposit afterward results when the treatedgases are brought into contact with the heated metals.

It is desirable that the gases at the time of contact with the charcoalor coke should be heated to a temperature not less than. that of theannealing itself, so that any cracking will occur during thispre-treatment. Also, it is desirable that the gases shall be preheated,in any event, before b eing brought into cpntact with the metal and itssuperficial oxide film, to a temperature closely approximating that ofthe metal itself.

The course of the two stages of operation 1s supervised by chemicalanalysis of the entering and out-going gases, and by regulating the iiowvolume according to the compositions determined. It will be noted thatthe annealing is progressing during the entire period of the superficialoxidation and reduction,

' and may continueifor even longer periods fili since the annealing maybe begun and the metal kept at annealing temperature for a periodprevious to the oxidation step: between the oxidation and reductionstages: and following the reduction stage: and in especial it ispreferred to leave the metal in the presence of the stabilizedhydrocarbon gas during its cooling so that the hot metal is not broughtinto contact with the atmosphere. f

It is found inpractice that the present method makes it possible to takea piece of smooth but badly discolored metal, having oxide, oily andother carbonaceous streaks on its'surface, and by a very simple, directand progressive operation, to bring forth the metal clean and bright,while it has been definitely annealed and softened for later working.

Two examples of the practice according to this invention are set forthby way of illustration on the accompanying drawings, in which:

Figure 1 is a diagrammatic view showing the simultaneous annealing andcleaning by a batch process in'a pit-type furnace.

Fig. 2 is a corresponding diagrammatic view showing the continuous andsimultaneous annealing and cleaning of a continuous wire.

Examples of the employment of the invention may now be set forth inconjunction with the showing of the illustrative forms in thesedrawings:

E ample I A charge of metal such as brass or copper is placed, forexample, in the pot of a pittype furnace 11, wherein the pot may beheated to the desired temperature. A cover 12 for the pot has an inlettube 13 passing downwardly therethrough and terminating in a flat coil14 at the base of the pot, while a frame 15 is indicated above this coilto provide a chamber 15a for the distribution of the incoming gas. Thecover 12 also has an outlet tube 16`and an aperture 17 which is fittedwith a charging lid 18. The gas inlet pi e 13 is connected through athree-way va ve 19 with a container 20 for carbon dioxide or similaroxidizing gas, on the one hand, and on the other hand with a washingvessel 21 containing paraffin oil through which a stream of coke ovengas is passed from the main 22. The valve 19 serves to determine whetherthe carbon dioxide gas or the coke oven gas is being employed while therespective gases are controlled in volume by the regulating valves 23,24.

Assuming that the charge has an external surface of approximately 100square feet, and that its surface c olor is from brown to black instreak or solid color, indicating the presence of a discoloration ofrolled oil which maybe chemically regarded as a carbon compoundcontaining a very large proportion of carbon.

The charge of metal is brought by the furnace to a uniform temperatureof 850 to 13500 F. in the case of brass or copper, a preferredtemperature for such materials being 1300 F. The valve 19 is thenoperated and a regulating valve 23 opened so that carbon dioxide ispassed through the inlet pipe 13 and its coil 14 and thereby is heatedto the internal temperature of the furnace: to-wit 13000 F. The quantityof gas is regulated to correspond to the delivery of 0.44 cubic feet persquare foot of surface er hour. In the particular example, this ow iscontinued for ten minutes with a total delivery of 7.33 cubic feet ofcarbon dioxide. This flow of carbon dioxide is then discontinued.Heating may also be discontinued and after the contents of the furnacehave been cooled to 230 F. or below, the charge may be withdrawn withoutfear of excessive oxidation in the atmosphere.

The surface of the charge then presents an evenly distributed andthoroughly oxidized film over the entire area, being both annealed andcleaned of carbon. It is then ready for working if so desired: but itis, however, preferred that the surface should be bright, in most cases.

` For this purpose, the batch may be returned to the same furnace, orpreferably is left therein and the heating in the furnace continued at13000 F. The valve 19 has already been manipulated to shut oli the flowof carbon dioxide gas, and is now moved to admit the purified naturalgas from the pipe 22, which has had its unsaturated illuminantssubstantially removed in the paraffin bath 21. This gas is permitted toflow in at the rate of 0.33 cubic feet per hour per hundred square feetof surface area in the charge. This flow is continued for fifty minutes,a

Ewample I I The cleaning and bright annealing of brass or copper stripsor wire in a continuous strip type furnace is illustrated in Fig. ,2.,The coil delivers a strip 31 which passes through an oxidizing chamber32, a reducing chamber 33 and a cooling chamber 34, moving throughsubstantially gas-tight apertures in the partitions between therespective chambers. The chambers 32 and 33 are, for example, heated bythe electric coil 35, and are surrounded by a heat insulating jacket 36.The cooling chamber 34 has for example, a coil 37 surrounding it throughwhich water may be passed as desired. An externaly preheater 38 isprovided with a coil 39, which is connected through regulating valve 41with a'pump 42 by which atmospheric air is forced .through the coil 39and thence past a further regulating valve 43 into the interior of theoxidizing chamber 32, from which it may escape by the outlet pipe 44. uA heating means is provided for this preheater 38. Similarly, the citygas main 45 has branches therein of which the branches 46 lead to aburner 40 and to a burner 47 for heating the retort 48 containing alayer of heated charcoal 49 iu its base and having a central partitionwhich causes the flow of city gas from the branch pipe 50 past regugasbeing emlat-ing valve 51 through the charcoal 49- whereby theunsaturates thereof are substantially eliminated, and from which thetreated gas is delivered through the pipe 52 into the reducing chamber33 of the furnace from which -the same may escape by an outlet 54 orthrough a tap connection 55 into the cooling chamber 34, so that anon-oxidizing atmosphere may be maintained in this cooling chamberduring the, reduction of temperature of the strip from the annealingheat to the temperature of delivery.

The temperature of the furnace and Within the preheater and theabsorbent retort 48 is maintained at preferably 1300o F., and the speedof the. movement of metal through the furnace and cooling chambers isadjusted in such a. way that the time factors per square foot of surfaceare essentially the same as those set forth in Example I. It will benoted that chamber 32lis one-fifth of the length of chamber 33, andhence by maintaining uniform concentrations in the chambers 32 and 33,the proper proportion of action is obtained, and the strlp is subjectedto the carbon dioxide for tenminutes and to the hydrocarbon gas forfifty minutes.

It will be understood that the temperaturcs and proportions set forthabove are varied according to the characteristic of the metal which isbeing treated. Vith certain metals, for example, a temperature of 900 F.will produce the annealing necessary for obtaining a predetermined grainsize and hardness` of ,the iinished product. It the metal is alreadybright and free from carbonaceous discoloration, the first step of theoperation may be dispensed with, and the material treated immediatelywith the Yhydrocarbon gas, say at the rate of 33 cubic feet per hour forten minutes for a superficial area ot 100 square feet. The annealingprocedure proceeds during this time, and the material is then'cooledeither slowlyor quickly as required by the particular metal beingtreatedand is removed from the furnace. During this, the metal has beenmaintained in a perfectly bright and undiscolored condit-ion but is madesoft enough to permit further rolling, forging, stamping or forming. v

In experimental Work, it has been found that a gas layer ofapproximately onesixteenth of an inch thick surrounded the work in everyinstance mentioned, whether stationary in the pit-type furnace ordelivering through the continuous furnace: which by calculationindicates a velocity of 0.01915 feet per second, and giving a .gas layerof this thickness on the surface of this amount of work at anytemperature between 850 and 1350 F. v

Other metals may be treated lin the manner described, as for examplenickel, nickel silver '(so-called German silver), copper, brass, bronze,steel, iron, aluminum, and other alloys of these metals.

It will be understood that the invention is zoV y not limited to theparticular materials emfre'e from unsaturated hydrocarbons where-- by toreduce the said' oxide film but without the deposit of soot upon themetal.

2. The method of bright .annealing metals which comprises heating themetal to lan annealing temperature, bringing the metal while so heatedinto Contact with an oxidizing atmosphere, andv then bringing the metalWhile so heated into conta/ct Wlth a S reducing atmosphere free fromunsaturated hydrocarbons, and cooling the metal in the absence of airand unsaturated hydrocarbons.

In testimony whereof, We aHX our signatures.

ROBERT G. GUTHRIE. oso AR J. WOZASEK.

